Many studies have focused on diets that reduce calories via a low-carbohydrate (Atkins diet, Scarsdale diet, Zone diet) diet versus a low-fat diet (LEARN diet, Ornish diet). The Nurses’ Health Study, an observational cohort study, found that low carbohydrate diets based on vegetable sources of fat and protein are associated with less coronary heart disease.

A meta-analysis of randomized controlled trials by the international Cochrane Collaboration in 2002 concluded that fat-restricted diets are no better than calorie restricted diets in achieving long term weight loss in overweight or obese people. A more recent meta-analysis that included randomized controlled trials published after the Cochrane review found that “low-carbohydrate, non-energy-restricted diets appear to be at least as effective as low-fat, energy-restricted diets in inducing weight loss for up to 1 year. However, potential favorable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavorable changes in low-density lipoprotein cholesterol values when low-carbohydrate diets to induce weight loss are considered.”

The Women’s Health Initiative Randomized Controlled Dietary Modification Trial found that a diet of total fat to 20% of energy and increasing consumption of vegetables and fruit to at least 5 servings daily and grains to at least 6 servings daily resulted in:

• no reduction in cardiovascular disease
• an insignificant reduction in invasive breast cancer
• no reductions in colorectal cancer

Additional recent randomized controlled trials have found that:

• A comparison of Atkins, Zone diet, Ornish diet, and LEARN diet in premenopausal women found the greatest benefit from the Atkins diet.

• The choice of diet for a specific person may be influenced by measuring the individual’s insulin secretion:

In young adults “Reducing glycemic [carbohydrate] load may be especially important to achieve weight loss among individuals with high insulin secretion.” This is consistent with prior studies of diabetic patients in which low carbohydrate diets were more beneficial.

The American Diabetes Association released for the first time a recommendation (in its January 2008 Clinical Practice Recommendations) for a low carbohydrate diet to reduce weight for those with or at risk of Type 2 diabetes.